Oil-swellable elastomers have various applications in wells, especially wells used for producing hydrocarbons. For example, an oil-swellable elastomer can be used in downhole tools having swellable components, such as swellable packers. For another example, oil-swellable elastomers can be used as particulate in various hydraulic fracturing operations as part of a proppant matrix. In yet another example, an oil-swellable particulate can be used as a particulate in a gravel pack.
An oil-swellable elastomer swells when exposed to a fluid comprising a hydrocarbon. The elastomer swells as a hydrocarbon enters and is trapped in the elastomer matrix due to the natural affinity of the polymer molecules of the elastomer and the hydrocarbon. Oil is absorbed into the oil-swellable elastomer through diffusion. Through the random thermal motion of the atoms that are in the liquid hydrocarbons, oil diffuses into the elastomer. As hydrocarbon molecules are absorbed into the polymer matrix of the elastomer, it causes the elastomer to stretch and expand. Swelling of the elastomer in the presence of oil is irreversible (whereas water-swelling elastomer, which operates on osmosis phenomenon, is reversible process). The swelling continues until the internal stresses inside the elastomer reach equilibrium. That is, the swell pressure increases until diffusion can no longer occur.
Although the hydrocarbon of the fluids used for this purpose should not degrade the elastomer, they will alter its mechanical properties, such as hardness and tensile strength, depending on the volume increase.
An application of oil-swellable elastomers is in oil-swellable downhole tools such as swell screens used for sand control.
Sand control is an operation to reduce production of formation sand or other fines from a poorly consolidated subterranean formation. In this context, “fines” are tiny particles, typically having a diameter of 43 microns or smaller, that have a tendency to flow through the formation with the production of hydrocarbon fluids. The fines have a tendency to plug small pore spaces in the formation and block the flow of oil. As all the hydrocarbon is flowing from a relatively large region around the wellbore toward a relatively small area around the wellbore, the fines have a tendency to become densely packed and screen out or plug the area immediately around the wellbore. Moreover, the sand and fines are highly abrasive and can be damaging to pumping and oilfield other equipment and operations.
Placing a relatively larger particulate near the wellbore can help filter out the sand or fine particles and prevents them from flowing into the well with the produced fluids. The primary objective is to stabilize the formation while causing minimal impairment to well productivity. The particulate used for this purpose is referred to as “gravel.” In the oil and gas field, and as used herein, the term “gravel” is refers to relatively large particles ranging in diameter from about 0.1 mm up to about 2 mm. Generally, a particulate having the properties, including chemical stability, of a low-strength proppant is used in gravel packing. An example of a commonly used gravel packing material is sand having an appropriately large particulate size range.
In general, a mechanical screen is placed in the wellbore and the surrounding annulus is packed with a particulate of a larger specific size designed to prevent the passage of formation sand or other fines.
An example of such a mechanical swell screen is PETROGUARD™ Swell screens, which are commercially available from Halliburton Energy Services. PETROGUARD™ swell screens provide an alternative to traditional expandable sand-control techniques. The design combines Halliburton's SWELL TECHNOLOGY™ systems with bonded mesh filtration media provide a self-expanding screen which delivers the benefits associated with traditional expandable solutions, but with greatly reduced risk. The PETROGUARD™ swell screens utilize a base pipe with a sheath of an oil-swellable elastomer.
When the elastomer is formed into the form of a sheath around a piece of pipe or other tubular, the result of the swelling is an increase of the outside diameter of the oil-swellable elastomer on the tubular. The oil-swellable elastomer is developed by contact with oil in order to swell and seal between casing strings or pipe and open hole. Swelling of the packer is consistent along its length. Oil continues to diffuse into the elastomer causing the packing element to swell until it reaches the inside diameter of the open borehole. At this point a differentially sealing annular barrier can be created.
Operationally, the benefit of a swellable packer is simplicity. There are no moving parts required to work, through pipe manipulation or by applied hydraulic pressure. No special service personnel are needed. The packers are simply run to depth, similar to a casing, and allowed to swell before production or injection operations begin.
Previous solutions to swell oil-swelleable elastomer has taken more than 5 days for 90% of complete swelling and there is no solution available where 90% of complete swelling can take place in less than 5 days.